ive gone through your same situation. somebody just doesnt want to take proper care of the fish. its hard convincing them the right thing to do.
if your changing water everyday he could be shocked. from just sitting in unclean water for two weeks and then suddenly be changed to new fresh water every day. does you Aunt know that about how and when to do water changes? 25% every couple days.
its always good to have a master liquid test kit to test the water for nitrate, nitrite, and amoinia. there should be 0 nitrites, 0 ammonia, and less than 20ppm nitrate
sits at bottom, floats at top- if hes not moving its probly the heater thing. what do you/your aunt feed him? does his belly look bloated at all?